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Humulus lupulus

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Humulus lupulus, the common hop or hops, is a species of flowering plant in the hemp family, Cannabaceae. It is a perennial, herbaceous climbing plant which sends up new shoots in early spring and dies back to a cold-hardy rhizome in autumn.[2] It is dioecious (having separate male and female plants) and native to West Asia, Europe and North America.

Common hop
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Rosales
Family: Cannabaceae
Genus: Humulus
Species:
H. lupulus
Binomial name
Humulus lupulus
Synonyms[1]
  • Humulus cordifolius Miq.
  • Humulus volubilis Salisb. nom. illeg.
  • Humulus vulgaris Gilib.
  • Lupulus amarus Gilib.
  • Lupulus communis Gaertn.
  • Lupulus humulus Mill.
  • Lupulus scandens Lam. nom. illeg.
male inflorescences

As the female cone-shaped flowers (hops) are used to preserve and flavor beer, the species is widely cultivated for the brewing industry.[2]

Description

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Humulus lupulus is a perennial herbaceous plant up to 10 metres (33 feet) tall, living up to 20 years.[3] It has simple leaves with 3–5 deep lobes that can be opposite or alternate.[4] The species is triggered by the longer summer days to flower,[5] usually around July or August in the Northern Hemisphere.[6] The plant is dioecious, with male and female flowers on separate plants. The fragrant flowers are wind-pollinated.[7] The staminate (male) flowers do not have petals, while the pistillate (female) flowers have petals enveloping the fruit. The female flower cones (or strobili) are known as hops.[3] The fruit is an achene, meaning that it is dry and does not split open at maturity.[4] The achene is surrounded by tepals and lupulin-secreting glands are concentrated on the fruit.[8][9]

The species is sometimes described as a bine rather than a vine because it has stiff downward facing hairs that provide stability and allow it to climb.[3]

Chemistry

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H. lupulus contains myrcene, humulene, xanthohumol, myrcenoland linalool,[10] as well as less defined tannins and resin.

Hops are unique for containing secondary metabolites, flavonoids, oils, and polyphenols that impact the flavor of the products they are common in, such as beer.[11] The bitter flavors in hops can be accounted for by acids composed of prenylated polyketides (a group of secondary metabolites), which highly impact the taste of hop-based products.[12] Multiple genes have been identified as factors in the expression of taste including O-methyltransferase 1, geranyl diphosphate synthase, and chalcone synthase. Genomic analyses have shown evidence that the intervention of humans in the selection process of the hop over the thousands of years it has been cultivated have provided noticeable enhancements in aroma and bitterness as well as selection of varieties with high yield rates.[13]

Flowering, growth, and stress response

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Predicted genes in homologous primary contigs have been identified as accounting for various traits expressed via variation in the growth, flowering, and stress responses in the plant. These homologous primary contigs correspond to regions with large amounts of sequence variation. Genes in the hop that contain higher rates of sequence divergence in homologous primary contigs (overlapping DNA sequences inherited by a common ancestor) have been attributed to the expression of flowering, growth and responses to (both abiotic and biotic) stress in the plant. The responses to stress are thought to manifest in the distinct differences and difficulties in the cultivation processes between geographically popular varieties of the hop plant.[14] Outside environmental stress, such as changes in temperature and water availability has also been shown to significantly alter the transcriptome and incite reductions in genes known to be involved in the synthesis of secondary metabolites (including bitter acids), which are organic compounds produced that do not impact development or reproduction of hops. Environmental stress has also been shown to reduce expression of the valerophenone synthase gene, which is known to be an essential genetic component in the regulation of bitter acid production. This shows that impacts of outside stress on H. lupulus likely has a direct implication of the expression of the bitter flavor that remains an essential component of the popularity of the plant.[11]

Research

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  • Humulus lupulus contains xanthohumol, which is converted by large intestine bacteria into the phytoestrogen 8-prenylnaringenin, which may have a relative binding affinity to estrogen receptors[15] as well as potentiating effects on GABAA receptor activity[16]
  • Humulus lupulus extract is antimicrobial, an activity which has been exploited in the manufacture of natural deodorant.[17]
  • Spent H. lupulus extract has also been shown to have antimicrobial and anti-biofilm activities, raising the possibility this waste product of the brewing industry could be developed for medical applications.[18]
  • Extracts of the bitter alpha-acids present in H. lupulus have been shown to decrease nocturnal activity, acting as a sleep aide, in certain concentrations.[19]

Because of the growing understanding regarding the hop's overlap in gene structures with cannabidiolic acid synthase, the precursor structure to cannabidiol, there is a gap in general understanding about potential unknown compounds and benefits in hops. As the understanding of the health benefits available in cannabidiol increases, there is a growing demand to further investigate the overlap between cannabidiolic acid synthase and H. lupulus.[20]

Limitations
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The genome of H. lupulus is relatively large and has been shown to be a similar size to the human genome. The complexity of the hop genome has made it difficult to understand and identify unknown genetic properties, however with the growing availability of accessible sequencing, there is room for more advanced understanding of the plant.[20] Because of the growing concern of climate change, and the assumption that there will be an increase of heat waves, it is likely that growing large yields of hops could become more difficult. This could result in changes to the transcriptome of the hop, or result in a decrease of certain varieties, leaving less room for further research.[11]

Taxonomy

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Relation to Cannabis sativa

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The hop is within the same family of plants such as hemp and marijuana, called Cannabaceae.[14] The hop plant diverged from Cannabis sativa over 20 million years ago and has evolved to be three times the physical size.[21][22][13][23] The hop and C. sativa are estimated to have approximately a 73% overlap in genomic content.[24] The overlap between enzymes includes polyketide synthases and prenyltransferases.[25] The hop and C. sativa also have significant overlap in the cannabidiolic acid synthase gene, which is expressed in the tissues of the leaves in both plants.[14]

Varieties

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Cultivation of hops in Ystad 2017
 
'Golden' hop

The five varieties of this species (Humulus lupulus) are:

  • H. l. var. lupulus – Europe, western Asia
  • H. l. var. cordifolius – eastern Asia
  • H. l. var. lupuloides (syn. H. americanus) – eastern North America
  • H. l. var. neomexicanus – western North American.[26]
  • H. l. var. pubescens – midwestern and eastern North America[27][28]

Many cultivars are found in the list of hop varieties. A yellow-leafed ornamental cultivar, Humulus lupulus 'Aureus', is cultivated for garden use. It is also known as golden hop, and holds the Royal Horticultural Society's Award of Garden Merit (AGM).[29][30]

Etymology

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The genus name Humulus is a medieval name that was at some point Latinized after being borrowed from a Germanic source exhibiting the h•m•l consonant cluster, as in Middle Low German homele.

According to Soviet Iranist Vasily Abaev this could be a word of Sarmatian origin which is present in the modern Ossetian language (Ossetian: Хуымæллæг) and derives from proto-Iranian hauma-arayka, an Aryan haoma.[31]

From Sarmatian dialects this word spread across Eurasia, thus creating a group of related words in Turkic, Finno-Ugric, Slavic and Germanic languages (see Russian: хмель, Chuvash хăмла, Finnish humala, Hungarian komló, Mordovian комла, Avar хомеллег).

The specific epithet lupulus is Latin for "small wolf".[32] The name refers to the plant's tendency to strangle other plants, mainly osiers or basket willows (Salix viminalis), like a wolf does a sheep.[3] Hops could be seen growing over these willows so often that it was named the willow-wolf.[32]

The English word hop is derived from the Middle Dutch word hoppe, also meaning Humulus lupulus.[33]

Distribution and habitat

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The plant is native to Europe, western Asia and North America.[32]

It grows best in the latitude range of 38°–51° in full sun with moderate amounts of rainfall.[2]

Ecology

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The flowers attract butterflies,[32] amongst other insects.

Animal pests

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Diseases

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Main article: List of hop diseases

Toxicity

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H. lupulus can cause dermatitis to some who handle them. It is estimated that about 1 in 30 people are affected by this.[9]

Uses

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Main article: Hops

H. lupulus is first mentioned in 768 CE when King Pepin donated hops to a monastery in Paris. Cultivation was first recorded in 859 CE, in documents from a monastery in Freising, Germany.[34]

The chemical compounds found in H. lupulus are the main components in flavoring and bittering beer. The fragrant flower cones, known as hops, impart a bitter flavor and also have aromatic and preservative qualities.[35] Some other compounds help with creating foam in beer. Chemicals such as linalool and aldehydes contribute to the flavor of beer. The main components of bitterness in beer are iso-alpha acids, with many other compounds contributing to beer's overall bitterness.[36] Until the Middle Ages, many varieties of plant were used to flavor beer, including most commonly Myrica gale.[34] H. lupulus became favored because it contains preserving agents which prolong the viability of a brew.

In culture

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H. lupulus was voted the county flower of Kent in 2002 following a poll by the wild flora conservation charity Plantlife.[37]

References

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  1. ^ "Humulus lupulus L.". World Checklist of Selected Plant Families. Royal Botanic Gardens, Kew. Retrieved 2 February 2016 – via The Plant List. Note that this website has been superseded by World Flora Online
  2. ^ a b c Sewalish, Andrew. "Habitat & Adaptation". Humulus lupulus profile. Retrieved 2017-04-13.
  3. ^ a b c d Conway, Sean; Snyder, Reid (2008). "Humulus lupulus - Hops" (PDF). College Seminar 235 Food for Thought: The Science, Culture, & Politics of Food. Hamilton College. Retrieved July 31, 2008.
  4. ^ a b "Humulus lupulus (common hop, hops)". Go Botany. New England Wildflower Society. Retrieved 2017-04-13.
  5. ^ "HerbalGram: Hops (Humulus lupulus): A Review of its Historic and Medicinal Uses". cms.herbalgram.org. Retrieved 2017-04-08.
  6. ^ "Hop, Humulus lupulus - Flowers". NatureGate. Retrieved 2017-04-13.
  7. ^ "Hops, Humulus lupulus, plant facts". Eden Project. Retrieved 2017-04-12.
  8. ^ Burnham, Robyn J. (2014). "Vitis riparia". CLIMBERS: Censusing Lianas in Mesic Biomes of Eastern Regions. University of Michigan College of Literature, Sciences and the Arts. Retrieved 2017-04-02.
  9. ^ a b "Humulus lupulus". NewCROP, the New Crop Resource Online Program. Retrieved 2017-04-02.
  10. ^ Zanoli, Paola; Zavatti, Manuela (2008). "Pharmacognostic and pharmacological profile of Humulus lupulus L". Journal of Ethnopharmacology. 116 (3): 383–396. doi:10.1016/j.jep.2008.01.011. PMID 18308492.
  11. ^ a b c Eriksen, Renée L.; Padgitt-Cobb, Lillian K.; Townsend, M. Shaun; Henning, John A. (December 2021). "Gene expression for secondary metabolite biosynthesis in hop (Humulus lupulus L.) leaf lupulin glands exposed to heat and low-water stress". Scientific Reports. 11 (1): 5138. Bibcode:2021NatSR..11.5138E. doi:10.1038/s41598-021-84691-y. ISSN 2045-2322. PMC 7970847. PMID 33664420.
  12. ^ Goese, Markus; Kammhuber, Klaus; Bacher, Adelbert; Zenk, Meinhart H.; Eisenreich, Wolfgang (1999-07-15). "Biosynthesis of bitter acids in hops. A 13C-NMR and 2H-NMR study on the building blocks of humulone". European Journal of Biochemistry. 263 (2): 447–454. doi:10.1046/j.1432-1327.1999.00518.x. ISSN 0014-2956. PMID 10406953.
  13. ^ a b Natsume, S.; Takagi, H.; Shiraishi, A.; Murata, J.; Toyonaga, H.; Patzak, J.; Takagi, M.; Yaegashi, H.; Uemura, A.; Mitsuoka, C.; Yoshida, K. (2014-11-20). "The Draft Genome of Hop (Humulus lupulus), an Essence for Brewing". Plant and Cell Physiology. 56 (3): 428–441. doi:10.1093/pcp/pcu169. ISSN 0032-0781. PMID 25416290.
  14. ^ a b c Padgitt-Cobb, Lillian K.; Kingan, Sarah B.; Wells, Jackson; Elser, Justin; Kronmiller, Brent; Moore, Daniel; Concepcion, Gregory; Peluso, Paul; Rank, David; Jaiswal, Pankaj; Henning, John; Hendrix, David A. (2021-02-18). "A draft phased assembly of the diploid Cascade hop ( Humulus lupulus ) genome". The Plant Genome. 14 (1): e20072. doi:10.1002/tpg2.20072. ISSN 1940-3372. PMID 33605092. S2CID 231962731.
  15. ^ Milligan SR, Kalita JC, Heyerick A, Rong H, De Cooman L, De Keukeleire D (June 1999). "Identification of a potent phytoestrogen in hops (Humulus lupulus L.) and beer". J Clin Endocrinol Metab. 84 (6): 2249–52. doi:10.1210/jcem.84.6.5887. PMID 10372741.
  16. ^ Benkherouf, Ali Y.; Soini, Sanna L.; Stompor, Monika; Uusi-Oukari, Mikko (February 2019). "Positive allosteric modulation of native and recombinant GABAA receptors by hops prenylflavonoids". European Journal of Pharmacology. 852: 34–41. doi:10.1016/j.ejphar.2019.02.034. ISSN 0014-2999. PMID 30797788. S2CID 73456325.
  17. ^ "Hops [CO2] Extract". Toms of Maine. Archived from the original on December 24, 2013. Retrieved 2009-06-06.
  18. ^ Rozalski M, Micota B, Sadowska B, Stochmal A, Jedrejek D, Wieckowska-Szakiel M, Rozalska B (2013). "Antiadherent and Antibiofilm Activity of Humulus lupulus L. Derived Products: New Pharmacological Properties". BioMed Research International. 2013: 1–7. doi:10.1155/2013/101089. PMC 3794639. PMID 24175280.
  19. ^ Franco, L.; Sánchez, C.; Bravo, R.; Rodriguez, A.; Barriga, C.; Juánez, Javier Cubero (2012-06-01). "The sedative effects of hops (Humulus lupulus), a component of beer, on the activity/rest rhythm". Acta Physiologica Hungarica. 99 (2): 133–139. doi:10.1556/APhysiol.99.2012.2.6. ISSN 0231-424X. PMID 22849837.
  20. ^ a b "Advancing understanding of hop genome to aid brewers, medical researchers". ScienceDaily. Retrieved 2021-04-09.
  21. ^ Divashuk, Mikhail G.; Alexandrov, Oleg S.; Razumova, Olga V.; Kirov, Ilya V.; Karlov, Gennady I. (2014-01-21). "Molecular Cytogenetic Characterization of the Dioecious Cannabis sativa with an XY Chromosome Sex Determination System". PLOS ONE. 9 (1): e85118. Bibcode:2014PLoSO...985118D. doi:10.1371/journal.pone.0085118. ISSN 1932-6203. PMC 3897423. PMID 24465491.
  22. ^ Murakami, A; Darby, P; Javornik, B; Pais, M S S; Seigner, E; Lutz, A; Svoboda, P (2006-05-10). "Molecular phylogeny of wild Hops, Humulus lupulus L." Heredity. 97 (1): 66–74. doi:10.1038/sj.hdy.6800839. ISSN 0018-067X. PMID 16685279. S2CID 11920277.
  23. ^ Pisupati, Rahul; Vergara, Daniela; Kane, Nolan C. (2018-02-21). "Diversity and evolution of the repetitive genomic content in Cannabis sativa". BMC Genomics. 19 (1): 156. doi:10.1186/s12864-018-4494-3. ISSN 1471-2164. PMC 5822635. PMID 29466945.
  24. ^ Laverty, Kaitlin U.; Stout, Jake M.; Sullivan, Mitchell J.; Shah, Hardik; Gill, Navdeep; Holbrook, Larry; Deikus, Gintaras; Sebra, Robert; Hughes, Timothy R.; Page, Jonathan E.; van Bakel, Harm (2018-11-08). "A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci". Genome Research. 29 (1): 146–156. doi:10.1101/gr.242594.118. ISSN 1088-9051. PMC 6314170. PMID 30409771.
  25. ^ Marks, M. David; Tian, Li; Wenger, Jonathan P.; Omburo, Stephanie N.; Soto-Fuentes, Wilfredo; He, Ji; Gang, David R.; Weiblen, George D.; Dixon, Richard A. (2009-07-06). "Identification of candidate genes affecting Δ9-tetrahydrocannabinol biosynthesis in Cannabis sativa". Journal of Experimental Botany. 60 (13): 3715–3726. doi:10.1093/jxb/erp210. ISSN 1460-2431. PMC 2736886. PMID 19581347.
  26. ^ NRCS. "Humulus lupulus var. neomexicanus". PLANTS Database. United States Department of Agriculture (USDA). Retrieved May 5, 2016.
  27. ^ "Humulus lupulus". Germplasm Resources Information Network. Agricultural Research Service, United States Department of Agriculture. Retrieved 2018-07-31.
  28. ^ NRCS. "Humulus lupulus var. pubescens". PLANTS Database. United States Department of Agriculture (USDA).
  29. ^ "Humulus lupulus 'Aureus' AGM". RHS Plant Selector. Royal Horticultural Society. Retrieved 25 August 2020.
  30. ^ "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 43. Retrieved 3 March 2018.
  31. ^ Абаев В. И. Историко-этимологический словарь осетинского языка. Т. 4. М.—Л., 1989. С. 261-262.
  32. ^ a b c d "Humulus lupulus". Plant Finder. Missouri botanical Garden. Retrieved 2017-04-12.
  33. ^ Harper, Douglas. "hop". Online Etymology Dictionary.
  34. ^ a b Behre, Karl-Ernst (1999). "The history of beer additives in Europe - a review". Vegetation History and Archaeobotany. 8 (1–2): 35–48. doi:10.1007/BF02042841. S2CID 129429552.
  35. ^ Langezaal CR, Chandra A, Scheffer JJ (1992). "Antimicrobial screening of essential oils and extracts of some Humulus lupulus L. cultivars". Pharm Weekbl Sci. 14 (6): 353–356. doi:10.1007/bf01970171. PMID 1475174. S2CID 12561634.
  36. ^ Schönberger, C.; Kostelecky, T. (2011). "125th Anniversary Review: The Role of Hops in Brewing" (PDF). Journal of the Institute of Brewing. 117 (3): 259–267. doi:10.1002/j.2050-0416.2011.tb00471.x.
  37. ^ Plantlife website County Flowers page Archived 2015-04-30 at the Wayback Machine

Bibliography

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  • "Czech hop varieties". Žatec: Chmelařský institut, 2012. on-line
  • Barchet, Ron. "German hops in craft brewing". Wolnzach: Hopfen-Rundschau, 2014.
  • Biendl, Martin. "Hops and health". Wolnzach: German Hop Museum, 2013.
  • Hieronymus, Stan. "For the love of hops: The practical guide to aroma, bitterness and the culture of hops". Boulder, CO: Brewers Publications, a division of the Brewers Association, 2012.
  • Kopp, Sylvia. "Barley & hops: The craft beer book". Berlin: Gestalten, 2014.
  • Melnychuk, M. D.; Boyko, A. L.; Hryhoryuk, I. P.; Likhanov, A. F.; Klyuvadenko, A. A.; Martyn, H. H.; Kukovenko, V. I. "Hop (Humulus lupulus L.): From cell to plant". Kyiv: Printeko, 2013.
  • Nesvadba, Vladimír. "Development and tradition of Czech hop varietes". Žatec: Hop Research Institute, 2013.
  • Neve, Ray A. "Hops". London: Chapman and Hall, 1991.
  • Skomra, Urszula. "Polish hop cultivars". Puławy: Institute of Soil Science and Plant Cultivation, 2010.
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